The currently available cooling fan mainly includes a stator, a rotor, a circuit board, blades, a bearing, and a frame.
With the constantly increased applications of the cooling fan in different fields, from the central processing unit in electronic devices to servers, power supply devices, communication chassis, telecommunication base stations, etc., the cooling fan is frequently used in severe working environment, such as an environment with high humidity and salt fog. Since most of the currently available cooling fans are not provided with any structure for guarding against external moisture and salt fog, the stator and bearing inside the fan are subject to invasion by the moisture and salt fog and easily become corroded. In some worse condition, the circuit board of the fan is also corroded and becomes failed to shorten the fan service life.
To solve the above problems, two solutions have been proposed by those skilled in the art, namely, vacuum coating process and encapsulating process. In vacuum coating process, the stator and the circuit board are entirely coated with a film to obtain a waterproof effect. However, when the fan operates in an environment with salt fog, crystallized salt tends to grow and accumulate in the fan, the vacuum coated film, which is a very thin layer of polymeric compound, is subject to breaking when it is in frictional contact with the crystallized salt in the fan. As a result, electronic components in the fan are invaded by salty water and subject to short circuit and burnout.
In the encapsulating process, the stator and the circuit board are first assembled to the fan frame, and the obtained assembly is positioned in a mold. Then, a predetermined type of encapsulating compound is filled in the mold. After the encapsulating compound is set, the encapsulated assembly is removed from the mold. In this process, the encapsulating compound is filled into all spaces in the stator and the circuit board and encloses the whole stator and circuit board therein, so as to obtain the waterproof effect. A very thick capsule is formed in this process to enclose all the electronic components of the fan therein. Heat produced by the electronic components during operation thereof is not easily dissipated from the thick capsule to thereby cause burnout of the electronic components and failure of the fan.
The vacuum coating process and the encapsulating process are designed mainly for protecting the electronic components of the fan against corrosion by water and salt fog, but fail to prevent external moisture and salt fog from invading into the internal structure of the fan. Therefore, the vacuum coating process and the encapsulating process simply provide a way to protect the circuit board against water, and external water and salt fog can still invade the internal structure of the conventional fans. Moreover, when the fan motor is encapsulated to protect the circuits inside the fan, the heat produced by the motor during operation thereof can not be well dissipated from the capsule, which in turn brings constant rising temperature of the motor. The salt fog invaded into the fan and subjected to the high temperature tends to deposit and crystallize in the fan, and the crystallized salt attaches to the inner walls of the fan, resulting in stuck rotor shaft and bearing and burnt-out circuit board. Therefore, the cooling fan with the conventional ways of guarding against external water and salt fog has the following disadvantages: (1) having shortened service life; (2) having accumulated heat in the fan; and (3) having low heat dissipation efficiency.
It is therefore tried by the inventor to develop an improved fan with pressurizing structure to prevent external moisture and salt fog from entering the fan, so as to overcome the problems existed in the prior art fans.